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AGRICULTURE 


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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  286 


FERTILIZER  EXPERIMENTS  WITH 

GREENHOUSE  LETTUCE 

AND  TOMATOES 

BY  J.  W.  LLOYD 


URBANA,  ILLINOIS,  FEBRUARY,  1927 


SUMMARY 

The  experiments  in  the  production  of  greenhouse  lettuce  and  toma- 
toes reported  in  this  bulletin  were  designed  primarily  to  test  the  effec- 
tiveness of  various  forms  of  commercial  fertilizer  as  supplements  to  a 
soil  mixture  of  4  parts  brown  silt  loam,  2  parts  rotted  manure,  and  1 
part  sand.  However,  for  purposes  of  comparison  two  other  soil  mix- 
tures were  used,  and  also  the  effect  of  steam  sterilization  of  greenhouse 
soil  was  tested.  Four  crops  of  lettuce  and  one  crop  of  tomatoes  were 
grown  each  year. 

The  4-2-1  soil  mixture  supplemented  with  nitrate  of  soda  or  with 
dried  blood  produced  better  average  yields  of  lettuce  than  the  untreated 
4-4-1  soil  mixture  (4  parts  brown  silt  loam,  4  parts  rotted  manure,  1 
part  sand) ,  and  fully  as  good  average  yields  of  tomatoes. 

The  addition  of  acid  phosphate  to  the  nitrate  treatment  reduced 
the  yields  of  lettuce  but  increased  the  yields  of  tomatoes.  However, 
when  lime  was  added  to  the  nitrate  and  acid  phosphate  in  treating  the 
4-2-1  soil  mixture,  the  detrimental  effect  of  the  acid  phosphate  on  the 
lettuce  was  overcome  and  the  high  yield  of  tomatoes  maintained. 

Another  way  in  which  the  detrimental  effect  of  acid  phosphate 
on  the  lettuce  was  avoided  was  by  using  nitrate  alone  on  the  4-2-1  soil 
mixture  for  producing  the  lettuce,  and  then  applying  a  top-dressing  of 
acid  phosphate  for  the  tomatoes  after  the  lettuce  was  harvested.  This 
treatment  produced  considerably  higher  average  yields  in  both  lettuce 
and  tomatoes  than  the  4-4-1  soil  mixture  without  commercial  fertilizer, 
andjnearly  as  high  a  combined  yield  of  lettuce  and  tomatoes  as  the 
4-4-1  soil  mixture  treated  with  nitrate  for  the  lettuce  and  acid  phos- 
phate and  potassium  sulfate  for  the  tomatoes. 

Steam  sterilization  of  the  4-4-1  soil  mixture  increased  the  yield 
of  lettuce  but  so  decreased  the  yield  of  tomatoes  that  the  combined 
yield  of  the  two  crops  was  considerably  less  than  from  the  unsterilized 
soil  of  the  same  composition,  and  also  much  less  than  from  the  4-2-1 
mixture  treated  with  nitrate  alone. 

In  the  light  of  these  experiments  it  is  recommended  that  in  grow- 
ing a  combined  crop  of  greenhouse  lettuce  and  tomatoes  on  brown  silt 
loam  in  raised  benches,  a  4-2-1  soil  mixture  be  employed,  and  that  this 
soil  be  fertilized  by  using  nitrate  of  soda  (approximately  .86  of  a 
pound  per  100  square  feet  of  bench  space)  before  planting  each  crop 
of  lettuce,  and  by  applying  a  top-dressing  of  acid  phosphate  (approxi- 
mately 2.3  pounds  per  100  square  feet  of  bench  space)  for  the  tomatoes 
after  the  last  crop  of  lettuce  for  the  season  has  been  harvested. 


FERTILIZER  EXPERIMENTS  WITH 

GREENHOUSE  LETTUCE 

AND  TOMATOES 

By  J.  W.  LLOYD,  Chief  in  Olericulture 

Greenhouse  vegetable  growers  in  Illinois  have  in  the  past  de- 
pended upon  stable  manure  almost  entirely  as  a  fertilizer  for  lettuce 
and  tomatoes.  During  the  last  few  years,  however,  it  has  become  more 
and  more  difficult  to  get  supplies  of  manure,  and  growers  have  been 
looking  for  a  method  of  producing  these  crops  without  the  use  of  as 
large  quantities  as  formerly. 

A  previous  experiment  at  the  Illinois  Station,1  in  which  garden 
loam  (brown  silt  loam),  rotted  manure,  and  sand  were  combined  in 
different  proportions  for  the  growing  of  greenhouse  lettuce  and  toma- 
toes, had  shown  that  with  every  increase  in  the  proportion  of  manure 
in  the  soil  mixture  there  was  an  increase  in  yield.  However,  the  soil 
composed  of  4  parts  garden  loam,  2  parts  rotted  manure,  and  1  part 
sand  (by  volume)  gave  good  yields  and  contained  sufficient  humus  to 
be  fairly  friable  and  retentive  of  moisture. 

The  essential  physical  conditions  for  good  growth  of  crops  appar- 
C  ently  being  supplied  by  this  amount  of  manure,  the  problem  became 
one  of  ascertaining  whether  the  plant-food  materials  in  the  mixture 
might  be  satisfactorily  supplemented  by  commercial  fertilizing  mate- 
rials so  as  to  provide  for  the  needs  of  maximum  crops.  Taking  the 
4-2-1  soil  mixture  as  standard,  therefore,  commercial  fertilizing  mate- 
rials containing  nitrogen,  potassium,  and  phosphorus  were  applied  to 
different  greenhouse  plots  and  the  yields  resulting  from  the  different 
treatments  recorded. 

A  comparison  was  also  made  between  soil  mixtures  containing 
different  proportions  of  manure,  both  with  and  without  commercial 
fertilizers,  and  a  test  was  included  to  determine  the  effect  of  sterilizing 
a  greenhouse  soil  with  steam  previous  to  the  planting  of  each  crop  of 
lettuce.  The  steam  sterilization  was  originally  planned  to  aid  in  dis- 
ease control,  but  as  there  was  very  little  damage  from  disease  in  any 
of  the  plots,  its  effect  on  the  yields  of  lettuce  was  of  more  significance. 

The  first  series  of  experiments  in  using  commercial  supplements 
to  manure  for  the  growing  of  greenhouse  lettuce  and  tomatoes  were 
conducted  for  three  years.  The  results,  reported  on  pages  317  to  328,  in- 
dicated that  certain  treatments  favorable  to  the  production  of  large 
yields  of  tomatoes  were  detrimental  to  the  lettuce  crop,  while  other 
treatments  favorable  to  lettuce  were  unfavorable  to  tomatoes.  There- 


Unpublished  data  in  experiment  by  C.  E.  Durst  and  H.  D.  Brown. 

[311] 


312  BULLETIN  No.  286  [February, 

fore,  further  tests  were  planned  with  a  view  to  finding,  if  possible,  a 
combination  of  treatments  that  would  be  effective  in  producing  large 
yields  of  both  crops.  These  are  reported  in  the  last  section  of  the 
bulletin,  on  pages  328  to  336. 

METHOD  OF  CONDUCTING  THE  EXPERIMENTS 

The  tests  were  made  in  the  west  greenhouse  of  the  vegetable  range 
at  this  Station.  The  house,  which  is  28  by  50  feet,  is  provided  with 
both  ridge  and  side  ventilation  and  equipped  with  four  benches.  Three 
of  the  benches  were  used  for  the  different  soil  treatments,  while  part 
of  the  fourth  was  employed  for  growing  the  young  plants  preparatory 


FIG.  1. — LETTUCE  SEEDLINGS  SOON  AFTER  BEING  SHIFTED  TO 

2:L2-lNCH   POTS 

With  both  lettuce  and  tomatoes,  the  seed  was  sown  in  flats 
and  the  young  seedlings  shifted  to  2V2-inch  pots  as  soon  as  the 
plants  were  large  enough  to  handle.  The  soil  used  in  the  pots  was 
in  all  cases  a  mixture  of  4  parts  garden  loam,  2  parts  manure, 
and  1  part  sand. 


to  setting  them  in  the  differently  treated  soil  mixtures.  The  benches 
were  47  inches  wide,  inside  measure,  and  were  divided  by  cross  parti- 
tions into  sections  6  feet  long,  so  that  the  area  of  each  section  was 
approximately  24  square  feet.  The  depth  of  the  benches  was  6% 
inches. 

In  preparing  the  soil  mixture,  garden  loam  and  rotted  manure 
were  pulverized  by  passing  the  loam  thru  a  half-inch  screen  and  the 
manure  thru  a  manure  shredder.  The  loam,  manure,  and  sand  were 
then  thoroly  mixed  by  repeated  shoveling,  and  the  mixture  was  placed 
in  the  benches,  which  were  filled  slightly  above  the  level  of  the  sides. 
The  soil  was  smoothed  off  with  a  straight  edge  without  being  com- 
pacted. After  being  wet  down  and  prepared  for  planting,  the  top  of 
the  soil  was  slightly  below  the  edge  of  the  bench,  thus  leaving  suffi- 
cient space  for  watering. 


1937] 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


313 


Each  season  four  crops  of  Grand  Rapids  lettuce  and  a  spring  crop 
of  tomatoes  were  grown.  At  the  close  of  the  tomato  harvest  each  year 
the  benches  were  cleaned  out  completely  and  an  entirely  new  lot  of 
soil  put  in  for  the  next  season's  work. 

Method  of  Applying  Fertilizers.— In  applying  the  fertilizer  the  in- 
gredients for  each  section  were  weighed  separately,  ground  in  a  mortar, 
and  sprinkled  carefully  by  hand  over  the  surface  of  the  soil  in  the 
given  section  of  bench.  The  material  was  then  thoroly  mixed  with  the 


TABLE  1. — QUANTITIES  OF  FERTILIZER  APPLIED  TO  SOIL  IN  EXPERIMENTS  WITH 
GREENHOUSE  LETTUCE  AND  TOMATOES 


Fertilizer 

Amounts  applied1 

Per 
section 

Rate  per 
100  square 
feet 

Rate  per 
acre 

Nitrate  of  soda  

grams 
94 
432 
125 
250 
250 
500 

/6s. 
.860 
3.966 
1.147 
2.295 
2.295 
4.591 

Ibs. 
375 
1  728 
500 
1  000 
1  000 
2  000 

Dried  blood  

Potassium  sulfate  

Acid  phosphate  

Steamed  bone  

Lime  

:In  a  few  sections  double  the  above  quantities  of  nitrate  of  soda,  potassium  sul- 
fate, and  acid  phosphate  were  used. 

With  the  exception  of  the  nitrate,  only  one  application  was  made  for  the  season's 
cropping,  which  consisted  of  four  crops  of  lettuce  and  one  crop  of  tomatoes.  In  the 
case  of  the  nitrate  the  quantity  specified  was  usually  applied  previous  to  the  plant- 
ing of  each  lettuce  crop,  so  that  the  application  for  the  entire  season  ordinarily 
consisted  of  four  times  the  quantity  here  shown. 


soil  by  means  of  trowels.  The  fertilizer,  except  the  nitrate  of  soda, 
was  usually  applied  and  worked  into  the  soil  several  days  before 
the  planting  was  to  be  done.  The  nitrate  ordinarily  was  applied  not 
more  than  24  hours  before  the  planting.  As  soon  as  one  crop  of  let- 
tuce was  harvested,  the  soil  was  dug  up  with  a  hoe  and  leveled  with  a 
rake,  the  nitrate  applied,  and  another  crop  started  if  the  plants  were 
large  enough  for  setting.  Occasionally  it  was  necessary  to  wait  a  few 
days  for  the  plants  to  develop  to  the  proper  size  and  condition  for  set- 
ting. Usually,  however,  very  little  time  was  lost  between  the  harvest- 
ing of  one  lettuce  crop  and  the  planting  of  another. 

The  quantities  of  fertilizer  applied,  whether  used  alone  or  in  com- 
bination, were  in  most  instances  as  given  in  Table  1. 

Temperature  of  the  House. — After  the  warm  weather  of  early  fall 
was  over,  so  that  it  was  possible  to  control  the  temperature  in  the 


314  BULLETIN  No.  286  [February, 

house,  the  following  schedule  of  temperatures  was  maintained  in  the 
lettuce  house  until  the  third  crop  was  harvested:  night,  50°  F.;  cloudy 
day,  55°  F.;  clear  day,  60-65°  F.  When  the  fourth  crop  of  lettuce, 
which  was  interplanted  with  tomatoes,  was  put  on  the  benches,  the 
temperature  was  raised  5  degrees.  After  the  fourth  crop  of  lettuce 
was  harvested  and  the  tomatoes  occupied  the  benches  alone,  the  tem- 


FIG.  2. — LETTUCE  NEARLY  READY  TO  HARVEST 

The  lettuce  was  harvested  when  the  most  advanced  plants  had  reached 
prime  condition  for  market.  All  the  harvesting  was  done  in  the  morning, 
and  whenever  possible  on  a  cloudy  day,  in  order  to  lessen  the  variation  in 
weights  caused  by  differences  in  turgidity  of  lettuce  harvested  at  different 
hours  of  the  day  and  at  different  temperatures. 


perature  was  raised  to  the  following  schedule:  night,  65°  F.;  cloudy 
day,  70°  F.;  clear  day,  75-80°  F. 

Growing  the  Seedling  Plants. — For  growing  the  plants  of  both 
lettuce  and  tomatoes,  the  seed  was  sown  in  flats  and  the  young  seed- 
lings were  shifted  to  2% -inch  pots  as  soon  as  the  plants  were  large 
enough  to  handle.  The  potting  soil  used  was  in  all  cases  the  4-2-1 
mixture  described  on  page  311.  The  pots  were  plunged  to  their  rims  in 
the  soil  of  a  greenhouse  bench.  The  lettuce  plants  were  transplanted 
from  the  2l/2  -inch  pots  to  the  benches,  but  the  tomato  plants  were 
shifted  to  4-inch  pots  before  being  benched.  When  conditions  were 
favorable,  the  seed  for  the  first  crop  of  lettuce  was  sown  from  August 
19  to  25.  For  the  succeeding  crops  a  new  batch  of  seed  was  sown  at 
about  the  time  the  plants  of  the  preceding  crop  were  placed  on  the 
benches.  The  tomato  seed  was  sown  at  or  about  the  same  date  as  the 
lettuce  for  the  fourth  crop. 


1927} 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


315 


Distance  of  Planting. — The  soil  of  each  section  was  marked  off  in 
checks  8  inches  apart,  and  a  lettuce  plant  was  placed  at  each  intersec- 
tion. Each  section  thus  accommodated  six  rows  of  9  plants  each,  or  a 
total  of  54  plants.  When  the  tomatoes  were  interplanted  in  the  lettuce, 
4  lettuce  plants  were  omitted  from  the  second  row  and  4  from  the  fifth 
row,  and  tomato  plants  were  sub- 
stituted for  them.  Thus  for  the 
fourth  crop  there  were  46  lettuce 
plants  and  8  tomato  plants  in  each 
section. 

Care  of  the  Growing  Crops. — 
The  crops  were  carefully  watered 
and  cultivated  as  often  as  was 
necessary.  The  soil  without  ma- 
nure required  more  frequent  wa- 
tering than  that  with  manure. 
After  the  lettuce  had  begun  to 
cover  the  benches,  the  hose  was 
handled  in  a  manner  to  avoid  wet- 
ting the  leaves.  Fumigation  for 
the  control  of  aphids  and  white 
fly  was  resorted  to  whenever  con- 
ditions demanded  it. 

The  tomatoes  were  pruned  to 
single  stems,  and  were  trained  to 
perpendicular  cords  fastened  to 
wire  loops  that  extended  thru  the 
cracks  between  the  bottom  boards 
of  the  benches,  where  they  were 

anchored  by  means  of  small  wooden  blocks.  The  tops  were  tied  to 
horizontal  wires  supported  by  the  framework  of  the  house.  The  vines 
were  tied  to  the  upright  cords  by  means  of  soft  twine.  Hand  pollina- 
tion was  resorted  to  in  order  to  insure  setting  of  the  fruit. 

Harvesting. — When  the  most  advanced  lettuce  had  reached  prime 
condition  for  market,  the  entire  crop  was  harvested.  The  plants  were 
cut  off  at  the  surface  of  the  ground,  and  any  dried  or  yellow  leaves 
were  removed.  The  net  trimmed  lettuce  from  each  section  was  weighed 
separately  and  the  yield  recorded.  The  weights  of  the  four  crops  from 
a  given  plot  were  added  to  determine  the  yield  for  the  season. 

The  harvesting  was  invariably  done  in  the  morning,  and  when- 
ever possible  a  cloudy  day  was  chosen,  so  that  there  might  be  less 
variation  in  weights  due  to  differences  in  the  turgidity  of  lettuce  at 
different  hours  of  the  day  and  at  different  temperatures. 


FIG.    3. — TOMATO   PLANT   IN    4-lNCH 

POT,  READY  TO  SET  IN  BENCH 
The  lettuce  plants  were  trans- 
planted from  the  2^inch  pots  to  the 
benches,  but  the  tomato  plants  were 
shifted  to  4-inch  pots  before  being 
benched. 


316 


BULLETIN  No.  286 


[February, 


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EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


317 


The  tomatoes  were  harvested  twice  a  week,  beginning  as  soon  as 
there  were  any  ripe  fruits  and  continuing  as  long  as  there  were  any 
fruits  of  marketable  quality.  After  each  picking  they  were  graded 


TABLE  3. — DATES  OF  SOWING,  SHIFTING,  BENCHING,  AND  HARVESTING  TOMATOES 


1918-19 

1920 

1921 

1922 

1922-23 

1924 

Seed  sown  

Dec.  28 

Feb.  19 

Jan.  14 

Jan.  11 

Dec  28 

Jan   12 

Shifted  to  25-inch  pots.  .  . 
Shifted  to  4-inch  pots  

Jan.  6 
Feb.  8 

Mar.  8 
Apr.  1 

Jan.  29 
Feb.  23 

Jan.  30 
Feb  18 

Jan.  7 
Feb  3 

Jan.  26 
Feb  25 

Benched  

Feb.  22 

Apr.  10 

Mar  12 

Mar  4 

Feb  24 

Mar  15 

First  picking  

May  13 

June  18 

May  17 

May  12 

May  4 

May  27 

Last  picking  

July  30 

Aug.  30 

July  27 

Aug.  1 

Julv31 

Aug.  12 

Duration  of  harvest  

78  days 

73  days 

71  days 

81  days 

88  days 

77  days 

into  No.  1's,  No.  2's,  and  culls,  consideration  being  given  to  size,  shape, 
and  smoothness.  The  No.  1's  and  No.  2's  were  marketed  together  as  a 
single  grade,  and  met  with  ready  sale  in  the  local  market. 

The  dates  of  sowing,  shifting,  benching,  and  harvesting  the  vari- 
ous crops  of  lettuce  and  tomatoes  are  given  in  Tables  2  and  3. 


COMMERCIAL  FERTILIZERS  TESTED  AS  SUPPLEMENTS 

TO  MANURE 

In  the  following  analysis  of  the  results  obtained  in  the  first  three 
years  of  these  fertilizer  tests,  the  yields  for  the  lettuce  crops  and  for 
the  tomato  crops  are  given  separately.  As  previously  stated,  some 
treatments  proved  of  benefit  for  one  crop  but  detrimental  to  the 
other,  and  it  is  worth  while  to  see  just  what  these  results  were  before 
considering  the  later  tests  designed  to  discover  combination  treatments 
beneficial  to  both  crops. 

The  treatments  given  the  different  plots  in  this  first  series  of  tests 
are  shown  in  Table  4. 


EFFECT  OF  TREATMENTS  ON  YIELDS  OF  LETTUCE 


NITRATE  OF  SODA,  DRIED  BLOOD,  ACID  PHOSPHATE,  AND  POTASSIUM  SULFATE 
TESTED  SINGLY  AND  IN  COMBINATION 

The  results  of  supplementing  the  4-2-1  soil  mixture  with  a  single 
fertilizing  element  are  shown  in  Table  5,  which  gives  the  total  yields 
of  lettuce  from  certain  plots  each  year,  together  with  the  three-year 
average.  The  addition  of  nitrate  of  soda  invariably  increased  the 
season's  yield;  and  the  addition  of  dried  blood  gave  a  marked  increase 


318 


BULLETIN  No.  286 


[February, 


TABLE  4. — SOIL  TREATMENT  OF  THE  DIFFERENT  PLOTS  IN  LETTUCE  AND 
TOMATO  EXPERIMENTS,  1918-1921 


Plot 

Soil 
mixture1 

Treatment 

51 

4-2-1 

Check 

52 

4-2-1 

Nitrate  of  soda 

53 

4-2-1 

Dried  blood 

54 

4-2-1 

Acid  phosphate 

55 

4-2-1 

Potassium  sulf  ate 

56 

4-2-1 

Nitrate  (double  quantity) 

57 

4-2-1 

Acid  phosphate  (double  quantity) 

58 

4-2-1 

Acid  phosphate,  lime 

59 

4-2-1 

Acid  phosphate,  potassium  sulfate 

60 

4-2-1 

Acid  phosphate,  nitrate 

61 

4-2-1 

Potassium  sulfate,  nitrate 

62 

4-2-1 

Acid  phosphate,  potassium  sulfate,  nitrate 

63 

4-2-1 

Acid  phosphate,  potassium  sulfate,  nitrate  (double  quanti- 

ties) 

64 

4-0-1 

Check 

65 

4-0-1 

Acid  phosphate,  potassium  sulfate,  nitrate 

66 

4-0-1 

Acid  phosphate,  potassium  sulfate,  nitrate  (double 

quantities) 

67 

4-4-1 

Check 

68 

4-4-1 

Sterilized 

69 

4-4-1 

Acid  phosphate,  potassium  sulfate,  nitrate 

JIn  this  indication  of  the  soil  mixture  the  first  figure  refers  to  the  proportion  of 
garden  loam,  the  second  to  the  proportion  of  manure,  and  the  last  to  the  proportion 
of  sand.  These  proportions  were  determined  by  volume  rather  than  by  weight. 


in  yield  two  seasons  and  a  very  slight  decrease  the  third,  with  an  aver- 
age increase  of  7%  pounds.  On  the  other  hand,  the  addition  of  acid 
phosphate  or  potassium  sulfate  resulted  in  a  lower  average  yield. 

When  nitrogen  was  added  as  one  of  two  fertilizing  elements  to  the 
4-2-1  soil  mixture,  the  average  yield  for  the  three  years  was  slightly 
increased,  altho  not  so  much  as  when  nitrogen  alone  was  used  (Table 


TABLE  5. — YIELDS  OF  LETTUCE:    EFFECT  OF  ADDING  DIFFERENT  FERTILIZING 
ELEMENTS  SINGLY  TO  A  4-2-1  SOIL  MIXTURE 


Plot1 

Treatment 

1918-19 

1919-20 

1920-21 

3-year 
average 

51 

Check  

Ibs.  —  oz. 
56—  0 

Ibs.  —  oz. 
56—  8 

Ibs.  —  oz. 
49—  6 

Ibs.  —  oz. 
53—15 

52 

Nitrate  of  soda  

62—  5 

69—15 

58—14 

63—11 

53 

Dried  blood  

64—11 

71—10 

48—  0 

61—  7 

54 

Acid  phosphate  

57  —  15 

53  —  6 

47—  0 

52—12 

55 

Potassium  sulfate  

57—12 

51—  2 

41—15 

50—  4 

JEach  plot  represents  a  bench  area  of  approximately  24  square  feet. 


1927] 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


319 


6).  The  use  of  a  combination  of  acid  phosphate  and  potassium  sul- 
fate  resulted  in  a  slightly  larger  yield  one  year  and  a  very  slightly 
larger  three-year  average.  The  complete  fertilizer,  composed  of  acid 


TABLE  6. — YIELDS  OF  LETTUCE:    EFFECT  OF  ADDING  Two  OR  MORE 
FERTILIZING  ELEMENTS  TO  A  4-2-1  SOIL  MIXTURE 


Plot 

Treatment 

1918-19 

1919-20 

1920-21 

3-year 
average 

51 

Check  

Ibs.  —  oz. 
56—  0 

Ibs.  —  oz. 
56  —  8 

Ibs.  —  oz. 
49—  6 

Ibs.  —  oz. 
53  —  15 

59 
60 

Acid  phosphate,  potassium  sulfate  .  .  . 
Acid  phosphate,  nitrate  

58—15 
64  —  2 

56—  6 
61  —  1 

48—  4 
43  —  2 

54—  8 
56—  2 

61 

Potassium  sulfate,  nitrate  

61  —  9 

67  —  14 

38  —  13 

56  —  1 

62 

Acid  phosphate,  potassium  sulfate, 
nitrate  

52—14 

66—  1 

39—  7 

52—13 

phosphate,  potassium  sulfate,  and  nitrate  of  soda,  gave  a  marked  in- 
crease in  yield  one  year  but  such  small  yields  the  other  two  years  that 
the  three-year  average  was  below  that  of  the  check. 


LIME  COUNTERACTS  INJURIOUS  EFFECT  OF  ACID  PHOSPHATE 

Since  it  was  conceivable  that  acid  phosphate  might  render  the 
soil  too  acid  for  the  best  growing  conditions  for  the  lettuce,  one  plot 
was  treated  with  lime  in  addition  to  the  acid  phosphate  in  order  to 
compare  the  yields  with  those  from  the  plot  treated  with  acid  phos- 


TABLE  7. — YIELDS  OF  LETTUCE:  EFFECT  OF  ADDING  LIME  TO  PLOT  OF  4-2-1 
SOIL  MIXTURE  TREATED  WITH  ACID  PHOSPHATE 


Plot 

Treatment 

1918-19 

1919-20 

1920-21 

3-year 
average 

51 

Check  

/6s.  —  oz. 
56—  0 

/6s.  —  oz. 
56  —  8 

/6s.  —  oz. 
49—  6 

/6s.  —  oz. 
53—15 

54 

Acid  phosphate  

57—15 

53—  6 

47—  0 

52—12 

58 

Acid  phosphate,  lime  

58—14 

58—12 

56—  9 

58—  1 

phate  alone.  The  plot  to  which  lime  was  added  outyielded  the  plain 
acid-phosphate  plot  every  year  (Table  7) ,  and  as  an  average  for  the 
three  years  showed  more  than  5  pounds  increase  in  yield.  It  was  also 
distinctly  superior  to  the  check  plot,  while  the  plot  receiving  the  acid 
phosphate  alone  showed  a  lower  average  yield  than  the  check. 


320 


BULLETIN  No.  286 


[February, 


DOUBLING  THE  QUANTITY  OF  FERTILIZER  LOWERS  YIELD 

In  order  to  test  the  effect  of  supplying  plant  food  in  extra-large 
quantities,  a  few  plots  were  treated  with  double  the  amounts  used  in 
most  of  the  tests. 

The  double  nitrate  treatment  gave  lower  yields  than  the  normal 
nitrate  treatment  every  year  (Table  8),  and  as  an  average  for  the 
three  years  showed  a  decreased  yield  of  nearly  11  pounds.  The  aver- 
age yield  from  the  double  nitrate  plot  was  lower  than  from  the  check 
plot. 


TABLE  8. — YIELDS  OF  LETTUCE  WHEN  DOUBLE  THE  USUAL 
QUANTITIES  OP  FERTILIZERS  WERE  USED 


Plot 

Soil 
mix- 
ture 

Treatment 

1918-19 

1919-20 

1920-21 

3-year 
average 

51 

4-2-1 

Check  

Ibs.  —  oz. 
56—  0 

Ibs.  —  oz. 
56—  8 

Ibs.  —  oz. 
49—  6 

Ibs.  —  oz. 
53—15 

52 

4-2-1 

Nitrate  

62—  5 

69  —  15 

58—14 

63  —  11 

56 
54 

4-2-1 
4-2-1 

Nitrate  (double  quantity)  .  .  . 
Acid  phosphate  

53—  5 
57  —  15 

65—  2 
53  —  6 

34—  1 

47  —  0 

52—15 
52  —  12 

57 

4-2-1 

Acid  phosphate  (double 
quantity)  

58—  1 

50—  1 

46—  2 

51—  7 

62 

4-2-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  

52—14 

66—  1 

39—  7 

52—13 

63 

4-2-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  (double 
quantities)  

53—14 

59  —  10 

32—15 

48—13 

65 

4^0-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  

45—  3 

60—  5 

45—  8 

50—  5 

66 

4-0-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  (double 
quantities)  

42—  8 

62—14 

31—10 

45—11 

The  double  application  of  acid  phosphate  gave  a  slightly  lower 
three-year  average  yield  than  the  normal  application;  and  both  these 
treatments  resulted  in  lower  average  yields  than  the  check. 

Doubling  the  quantity  of  the  complete  fertilizer  (acid  phosphate, 
potassium  sulfate,  and  sodium  nitrate),  whether  used  on  a  soil  con- 
taining manure  or  without  manure,  decreased  the  average  yield  as 
compared  with  the  corresponding  plots  treated  with  the  normal  quan- 
tities of  the  same  ingredients. 


COMPARISON  OF  THE  THREE  SOIL  MIXTURES 

The  basic  soil  mixture  used  in  most  of  the  plots  was  composed 
of  4  parts  garden  loam,  2  parts  rotted  manure,  and  1  part  sand.  How- 
ever, three  plots  were  included  in  which  no  manure  was  added  to  the 


19271 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


321 


mixture  of  garden  loam  and  sand,  the  formula  being  4-0-1.  A  few 
plots  also  were  included  in  which  the  soil  mixture  was  composed  of  4 
parts  garden  loam,  4  parts  rotted  manure,  and  1  part  sand.  For  each 
of  these  soil  mixtures  there  was  an  untreated  check  plot  and  a  corre- 
sponding plot  treated  with  acid  phosphate,  potassium  sulfate,  and 
sodium  nitrate.  In  the  case  of  the  4-2-1  mixture  and  also  the  4-0-1 
mixture,  there  was  likewise  a  plot  receiving  a  double  treatment  of 
these  fertilizing  materials.  The  yields  from  these  various  plots  are 
given  in  Table  9. 


TABLE  9. — YIELDS  OF  LETTUCE:  COMPARISON  OF  THREE  SOIL  MIXTURES 
WITH  AND  WITHOUT  SUPPLEMENTAL  FERTILIZERS 


Plot 

Soil 
mix- 
ture 

Treatment 

1918-19 

1919-20 

1920-21 

3-year 
average 

• 

51 

4-2-1 

Check  

Ibs.  —  oz. 
56—  0 

Ibs.  —  oz. 
56  —  8 

Ibs.  —  oz. 
49—  6 

Ibs.  —  oz. 
53  —  15 

62 

4-2-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  

52—14 

66—  1 

39—  7 

52—13 

63 

4-2-1 

Acid  phosphate,   potassium 
sulfate,     nitrate  .  (double 
quantities)  

53—14 

59—10 

32—15 

48—13 

64 

4-0-1 

Check  

42—  0 

42—  1 

32—  3 

38—12 

65 

4-0-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  

45—  3 

60—  5 

45—  8 

50—  5 

66 

4-0-1 

Acid  phosphate,   potassium 
sulfate,     nitrate     (double 
quantities)  

42—  8 

62—14 

31—10 

45—11 

67 

4-4-1 

Check  

54—  6 

62—12 

56—  9 

57—14 

69 

4-4-1 

Acid  phosphate,   potassium 
sulfate,  nitrate  

47—  0 

69—  3 

50—  5 

55—  8 

Of  the  check  plots  the  one  with  the  4-4-1  mixture  gave  a  dis- 
tinctly larger  yield  than  the  4-2-1  mixture  in  two  of  the  three  years, 
and  as  a  three-year  average  showed  nearly  4  pounds  greater  yield.  The 
untreated  4-0-1  mixture  showed  an  average  yield  which  was  approxi- 
mately 19  pounds  less  than  the  4-4-1  mixture  and  15  pounds  less  than 
the  4-2-1  mixture. 

Treatment  with  the  complete  fertilizer  failed  to  increase  the  aver- 
age yields  from  the  4-2-1  mixture  and  from  the  4-4-1  mixture.  How- 
ever, the  addition  of  a  normal  quantity  of  the  complete  fertilizer  to  the 
4-0-1  mixture  increased  the  yield  every  year,  and  showed  a  gain  of 
more  than  11  pounds  as  a  three-year  average. 

The  double  quantity  of  complete  fertilizer  applied  to  the  4-0-1 
mixture  gave  an  increased  yield  two  years  of  the  three  and  an  in- 
crease of  approximately  7  pounds  as  a  three-year  average.  However, 


322 


BULLETIN  No.  286 


[February, 


the  4-0-1  mixture  with  a  complete  fertilizer  added,  yielded  less  than 
the  untreated  4-2-1  mixture  or  the  untreated  4-4-1  mixture.  Further- 
more, the  lettuce  produced  on  the  4-0-1  mixture  was  of  inferior  qual- 
ity, being  of  small  size  and  tough  in  texture. 

STEAM  STERILIZATION  INCREASES  YIELDS  OF  SECOND  AND  THIRD  CROPS 

Marked  increases  in  yield  were  secured  two  years  out  of  three 
from  a  plot  of  the  4-4-1  soil  mixture  which  was  sterilized1  with  steam 
before  the  planting  of  each  crop  of  lettuce,  that  is,  four  times  during 
each  cropping  season  (Table  10.)  The  three-year  average  yield  from 


TABLE  10. — YIELDS  OF  LETTUCE:  EFFECT  OF  STEAM  STERILIZATION 


Plot 

Treatment 

1918-19 

1919-20 

1920-21 

3-year 
average 

67 

Check  

tt>s.  —  oz. 
54—  6 

Ibs.—oz. 
62—12 

Ibs.  —  oz. 
56  —  9 

lb».  —  oz. 
57—14 

68 

Sterilized  

60—  0 

72—11 

54—14 

62—  8 

the  sterilized  plot  was  4  pounds  10  ounces  greater  than  from  the  cor- 
responding unsterilized  plot.  The  heavy  crops  of  lettuce  in  the  ster- 
ilized plots  were  distinctly  different  in  appearance  from  any  other  let- 
tuce in  the  house;  the  leaves  were  larger,  coarser,  and  darker  colored 
than  the  foliage  of  the  other  lettuce. 

The  increased  yield  from  the  sterilized  plot  was  due  largely  to 
the  especially  heavy  yields  in  the  second  and  third  crops  each  season. 
The  fourth  crop  of  the  season  was  sometimes  very  light  and  disap- 
pointing. The  repeated  sterilizing  seemed  to  render  the  plant  food  in  the 
manure  more  quickly  available,  so  that  the  supply  was  considerably 
depleted  by  the  time  the  fourth  crop  was  reached.  However,  the  ster- 
ilizing did  not,  on  the  average,  increase  the  yield  in  the  first  crop;  the 
principal  effect  was  on  the  second  and  third  crops  of  the  season. 

EFFECT  OF  TREATMENTS  ON  YIELDS  OF  TOMATOES 

During  the  harvesting  period  the  tomatoes  were  picked  twice  each 
week.  Except  in  1920,  when  a  late  start  was  secured  on  account  of 
delay  with  the  first  crop  of  lettuce  the  fall  before,  the  harvesting  of 
the  greenhouse  tomatoes  was  completed  by  the  time  the  main  crop  of 
outdoor  tomatoes  became  abundant.  The  total  yields  of  marketable 

*The  method  of  sterilization  was  as  follows:  A  galvanized  iron  pan  was  in- 
verted over  the  section  of  the  bench  to  be  sterilized,  and  live  steam  at  a  pressure 
of  about  5  pounds  was  introduced  under  the  pan  by  means  of  a  rubber  hose  con- 
nected with  a  steam  pipe  in  the  heating  system  of  the  greenhouse.  The  treat- 
ment was  continued  for  two  hours. 


1927] 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


323 


tomatoes  from  the  respective  plots  each  year  are  given  in  the  accom- 
panying tables. 

NITRATE  OF  SODA,  DRIED  BLOOD,  ACID  PHOSPHATE,  AND  POTASSIUM 
SULFATE  TESTED  SINGLY  AND  IN  COMBINATION 

The  effect  upon  tomato  yields  of  supplementing  the  4-2-1  soil  mix- 
ture with  a  single  element  of  plant  food  is  indicated  by  the  yields 
shown  in  Table  11. 


TABLE  11. — YIELDS  OF  TOMATOES:  EFFECT  OF  ADDING  DIFFERENT 
FERTILIZING  ELEMENTS  SINGLY  TO  A  4-2-1  SOIL  MIXTURE 


Plot 

Treatment 

Spring, 
1919 

Spring, 
1920 

Spring, 
1921 

3-year 
average 

51 

Check  

Ibs.  —  oz. 
58  —  13 

Ibs.  —  oz. 
45  —  6 

Ibs.  —  oz. 
53  —  14 

Ibs.  —  oz. 
52  —  11 

52 

Nitrate  

62—  4 

53—  0 

62  —  10 

59—  4 

53 

Dried  blood  

63—  8 

57—  1 

64  —  6 

61—10 

54 

Acid  phosphate  

54  —  8 

54  —  10 

61  —  13 

57  —  0 

55 

Potassium  sulfate  

51—14 

46—  0 

66—  8 

54—13 

The  plot  treated  with  nitrate  of  soda  and  the  one  treated  with 
dried  blood  invariably  gave  larger  yields  than  the  untreated  plot,  the 
average  increase  apparently  due  to  the  nitrate  treatment  amounting 
to  approximately  6%  pounds  to  the  plot  of  8  plants,  and  the  increase 
in  yield  apparently  due  to  the  dried  blood  amounting  to  almost  9 
pounds  to  the  plot.  The  two  plots  receiving  acid  phosphate  and  potas- 
sium sulfate  respectively  showed  increased  yields  two  years  out  of 
the  three,  and  increases  also  as  an  average  for  the  three  years. 

The  effects  on  the  yields  of  greenhouse  tomatoes  obtained  by  add- 
ing more  than  one  fertilizing  element  to  the  4-2-1  soil  mixture  are  in- 
dicated in  Table  12.  Wherever  nitrogen  was  included  in  the  fertilizer 
mixture,  the  average  yields  were  markedly  increased ;  and  where  nitro- 


TABLE  12. — YIELDS  OF  TOMATOES:    EFFECT  OF  ADDING  Two  OR  MORE 
FERTILIZING  ELEMENTS  TO  A  4-2-1  SOIL  MIXTURE 


Plot 

Treatment 

Spring, 
1919 

Spring, 
1920 

Spring, 
1921 

3-year 
average 

51 

Check  

Ibs.  —  oz. 
58—13 

Ibs.  —  oz. 
45—  6 

Ibs.  —  oz. 
53—14 

Ibs.  —  oz. 
52—11 

59 
60 

Acid  phosphate,  potassium  sulfate  .  .  . 
Acid  phosphate,  nitrate  

61—14 
67—  3 

44—13 
57—  0 

50—14 
67—  9 

52—  8 
63—15 

61 

Potassium  sulfate,  nitrate  

67—  2 

42—  5 

74—11 

61—  6 

62 

Acid  phosphate,  potassium  sulfate, 
nitrate  

64—  0 

52—  1 

61—12 

59—  4 

324 


BULLETIN  No.  286 


[February, 


gen  was  omitted,  the  average  yield  was  slightly  lowered.  A  compari- 
son with  the  yields  given  in  Table  11  shows  also  that  the  nitrate  of 
soda  used  in  conjunction  with  acid  phosphate  or  potassium  sulfate 
gave  larger  average  yields  of  tomatoes  than  when  nitrate  of  soda  was 
used  alone. 

ADDING  LIME  GIVES  NO  MATERIAL  INCREASE  IN  YIELD 

The  addition  of  lime  to  the  soil  treated  with  acid  phosphate  did 
not  materially  increase  the  average  yield  of  tomatoes  as  compared 
with  the  yield  from  the  plot  treated  with  acid  phosphate  alone  (Table 


TABLE  13. — YIELDS  OF  TOMATOES:     EFFECT  OF  ADDING  LIME  TO  PLOT  OF  4-2-1 
SOIL  MIXTURE  TREATED  WITH  ACID  PHOSPHATE 


Plot 

Treatment 

Spring, 
1919 

1919-20 

1920-21 

3-year 
average 

51 

Check  

Ibs.  —  oz. 
58—13 

Ibs.  —  oz. 
45—  6 

Ibs.  —  oz. 
53—14 

Ibs.  —  oz. 
52—11 

54 

Acid  phosphate  

54—  8 

54—10 

61—13 

57—  0 

58 

Acid  phosphate,  lime  

54—12 

57—  2 

60—11 

57—  8 

13).    Both  these  plots,  however,  gave  distinctly  higher  average  yields 
than  the  check  plot  of  the  same  kind  of  soil. 

o> 

DOUBLING   THE  QUANTITY  OF   FERTILIZER  LOWERS   YIELDS 

A  comparison  of  the  yields  of  tomatoes  from  plots  where  the  reg- 
ular quantities  of  the  fertilizing  materials  were  used,  with  those  from 
plots  receiving  double  those  quantities,  is  shown  in  Table  14.  In  no 
case  was  the  average  yield  increased  by  doubling  the  quantity  of  fer- 
tilizer; in  fact,  it  was  distinctly  smaller  in  three  cases  and  slightly 
smaller  in  the  other  than  the  yield  from  the  corresponding  nor- 
mally treated  plot.  The  decrease  in  yield  apparently  due  to  the  heavy 
fertilizing  was  especially  marked  in  the  case  of  the  soil  mixture  which 
contained  no  manure. 


COMPARISON  OF  THE  THREE  SOIL  MIXTURES 

The  check  plots  of  the  three  different  soil  mixtures  showed  marked 
differences  in  yields  of  tomatoes,  the  increase  in  yield  following  the  in- 
crease in  the  proportion  of  manure  in  the  mixture  (Table  15).  The 
untreated  4-2-1  mixture  gave  an  average  yield  of  over  11  pounds 
more  than  the  4-0-1  mixture,  while  the  4-4-1  mixture  gave  an  aver- 
age of  nearly  10  pounds  more  than  the  4-2-1  mixture.  The  differ- 


1927} 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


325 


TABLE  14. — YIELDS  OF  TOMATOES  WHEN  DOUBLE  THE  USUAL 
QUANTITIES  OF  FERTILIZERS  WERE  USED 


Plot 

Soil 
mix- 
ture 

Treatment 

Spring, 
1919 

1919-20 

1920-21 

3-year 
average 

51 

4-2-1 

Check  

Ibs.  —  02. 
58—13 

Ibs.  —  02. 
45—  6 

Ibs.  —  02. 
53  —  14 

Ibs.  —  02. 
52  —  11 

52 

4-2-1 

Nitrate  

62—  4 

53  —  0 

62  —  10 

59  —  10 

56 
54 

4-2-1 
4-2-1 

Nitrate  (double  quantity)  .  .  . 
Acid  phosphate  

65—  0 
54  —  8 

46—  0 
54  —  10 

66—  5 
61—13 

59—  2 
57  —  0 

57 

4-2-1 

Acid    phosphate    (double 
quantity)  

58  —  3 

46—  4 

54  —  9 

53  —  0 

62 

4-2-1 

Acid  phosphate,  potassium 
sulf  ate,  nitrate  

64—  0 

52  —  1 

61—12 

59  —  4 

63 

4-2-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  (double 
quantities)  

56  —  4 

50  —  2 

62  —  4 

56  —  3 

65 

4-0-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  

67—  8 

39—  8 

54—14 

53—15 

66 

4-0-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  (double 
quantities)  

58—  2 

40—  6 

31—12 

43—  7 

ence  in  average  yield  between  the  4-0-1  mixture  and  the  4-4-1  mixture 
was  21  pounds  and  8  ounces  per  plot,  or  more  than  2%  pounds  per 
plant.  In  other  words,  the  heavily  manured  plot  yielded  over  50 
percent  more  than  the  plot  without  manure. 

When  a  complete  fertilizer  was  added  in  normal  amount,  the  re- 
sponse to  the  fertilizer  treatment  was  greatest  in  the  case  of  the  soil 
without  manure,  on  which  the  increase  in  average  yield  apparently  due 
to  the  commercial  fertilizers  was  nearly  13  pounds  to  the  plot.  The 


TABLE  15. — YIELDS  OF  TOMATOES:  COMPARISON  OF  THREE  SOIL  MIXTURES, 
WITH  AND  WITHOUT  SUPPLEMENTAL  FERTILIZERS 


Plot 

Soil 
mix- 
ture 

Treatment 

Spring, 
1919 

1919-20 

1920-21 

3-year 
average 

51 

4-2-1 

Check  

Ibs.  —  02. 
58—13 

Ibs.  —  02. 
45—  6 

Ibs.  —  02. 
53—14 

Ibs.  —  02. 
52—11 

62 

4-2-1 

Acid    phosphate,  potassium 
sulfate,  nitrate  

64—  0 

52—  1 

61—12 

59—  4 

64 

4-0-1 

Check  

44—  1 

41—10 

37—  4 

41—  0 

65 

4-0-1 

Acid  phosphate,  potassium 
sulfate,  nitrate  

67—  8 

39—  8 

54—14 

53—15 

67 

4-4-1 

Check  

71—14 

52—  4 

63—  7 

62—  8 

69 

4-4-1 

Acid  phosphate,   potassium 
sulfate,  nitrate  

70—  3 

58—12 

73—  2 

67—  6 

326 


BULLETIN  No.  286 


[February, 


increase  in  average  yield  in  the  4-2-1  mixture,  apparently  due  to  the 
same  fertilizer  treatment,  was  only  6  pounds  and  9  ounces,  or  approx- 
imately half  as  much  as  in  the  case  of  the  soil  without  manure.  The 
commercial  fertilizer  gave  a  still  smaller  increase  when  added  to  the 
4-4-1  mixture,  the  difference  in  average  yield  evidently  due  to  the  fer- 
tilizer treatment  being  only  4  pounds  and  14  ounces  for  the  plot. 

STEAM  STERILIZATION  REDUCES  YIELD  OF  TOMATOES  FOLLOWING 
FOUR  CROPS  OF  LETTUCE 

The  yield  of  tomatoes  from  the  sterilized  plot  was  invariably 
lower  than  that  from  the  unsterilized  plot,  the  three-year  average 
showing  a  difference  of  more  than  15  pounds  in  favor  of  the  unster- 
ilized plot  (Table  16).  As  mentioned  in  the  discussion  regarding  the 


TABLE  16. — YIELDS  OF  TOMATOES:  EFFECT  OF  STEAM  STERILIZATION 


Plot 

Treatment 

Spring, 
1919 

1919-20 

1920-21 

3-year 
average 

67 

Check  

Ibs.—  oz. 
71—14 

Ibs.  —  oz. 
52—  4 

Ibs.  —  oz. 
63—  7 

Ibs.  —  02. 

62—  8 

68 

Sterilized  

46—  3 

51—  2 

43—  6 

46—14 

lettuce  on  the  sterilized  plot,  this  treatment  seemed  to  render  the  plant 
food  in  the  soil  mixture  more  quickly  available,  so  that  it  was  drawn 
upon  very  heavily  by  the  second  and  third  crops  of  lettuce.  This 
sometimes  left  little  available  plant  food  for  the  fourth  crop  of  lettuce 
and  the  crop  of  tomatoes  following  the  lettuce  on  the  sterilized  plot. 

COMBINED  YIELDS  OF  LETTUCE  AND  TOMATOES 

Since  it  is  desirable  to  know  the  total  yield  of  greenhouse  crops 
from  a  given  bench  area  during  the  greenhouse  cropping  season,  the 
average  yields  of  lettuce  and  marketable  tomatoes  per  season  from 
each  plot  or  bench  section  have  been  calculated  in  terms  of  pounds  per 
square  foot  of  bench  area  (Table  17).  The  average  total  yield  of  let- 
tuce and  tomatoes  combined  is  also  given. 

The  lettuce  and  tomatoes  were  sold  at  wholesale  to  merchants  in 
Champaign  and  Urbana.  The  price  received  for  the  lettuce  ranged 
from  12%  to  25  cents  a  pound,  averaging  slightly  over  20  cents. 
Twenty  cents  a  pound  was  approximately  the  average  price  received 
for  the  tomatoes  also;  they  sold  at  25  cents  a  pound  early  in 
the  season,  20  cents  later  on,  and  finally  at  15  cents  after  the  local 
early  outdoor  crop  was  supplying  the  market.  At  20  cents  a  pound 
for  both  crops,  four  plots  yielded  a  gross  income  of  more  than  one 


1927} 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


327 


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328  BULLETIN  No.  286  [February, 

dollar  for  each  square  foot  of  bench  space,  and  the  fifth  plot  yielded 
almost  one  dollar  a  square  foot,  while  the  poorest  plot  (the  check  plot 
without  manure  or  fertilizer)  yielded  products  worth  only  a  fraction 
more  than  66  cents  a  square  foot. 

The  lettuce  and  tomatoes  did  not  respond  equally  well  to  the  same 
fertilizer  treatment  (Table  17).  The  lettuce  responded  especially  well 
to  nitrogen  alone,  whether  it  was  supplied  by  means  of  sodium  nitrate, 
dried  blood,  heavy  manuring,  or  steaming  of  the  heavily  manured  soil. 
Acid  phosphate  seemed  to  be  detrimental  to  the  lettuce  crop  unless 
supplemented  by  lime  or  sodium  nitrate;  and  even  then  the  yields 
were  less  than  from  the  use  of  nitrate  alone.  The  complete  fertilizer, 
consisting  of  acid  phosphate,  potassium  sulfate,  and  sodium  nitrate, 
apparently  reduced  the  yields  of  lettuce,  except  on  the  soil  which  con- 
tained no  manure. 

On  the  other  hand,  the  tomatoes,  while  responding  quite  favorably 
to  the  nitrogen  treatment,  gave  considerably  higher  yields  where  the 
nitrate  was  supplemented  with  acid  phosphate,  and  the  highest  yield 
of  all  where  the  complete  fertilizer  was  used  on  the  plot  already  heav- 
ily manured.  Reasonable  quantities  of  acid  phosphate,  whether  used 
alone  or  in  combination,  apparently  were  not  detrimental  to  the  to- 
mato crop. 

It  would  appear  from  these  results  that  no  acid  phosphate  should 
be  used  for  the  lettuce  crop,  except  possibly  in  combination  with  lime, 
and  that  acid  phosphate  used  with  plenty  of  nitrogen  is  a  very  desir- 
able combination  for  the  production  of  good  crops  of  greenhouse  toma- 
toes. In  view  of  these  circumstances,  additional  tests  were  planned 
for  the  purpose  of  finding,  if  possible,  a  method  of  fertilizing  that 
would  be  highly  beneficial  to  both  crops.  These  further  tests  are  dis- 
cussed in  the  following  pages. 


To  obviate  the  harmful  effect  of  acid  phosphate  on  lettuce  noted 
in  the  preceding  experiments,  and  yet  furnish  phosphorus  for  the  suc- 
ceeding tomato  crop,  three  methods  of  supplying  this  plant  food  were 
compared:  (1)  lime  was  applied  along  with  the  acid  phosphate;  (2) 
steamed  bone  meal  was  substituted  for  acid  phosphate;  and  (3)  acid 
phosphate  was  applied  as  a  top-dressing  to  the  tomatoes  after  the  last 
crop  of  lettuce  was  harvested. 

In  the  earlier  tests  steam  sterilization  of  the  soil,  while  resulting 
in  heavy  initial  crops  of  lettuce,  seemed  to  effect  such  depletion  of  the 
soil  that  the  fourth  crop  of  lettuce  and  the  crop  of  tomatoes  were 
sometimes  greatly  reduced.  An  effort  was  made  to  overcome  this  dif- 


1927] 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


329 


ficulty  by  applying  nitrate  for  the  fourth  crop  of  lettuce,  and  then 
using  a  top-dressing  of  acid  phosphate  for  the  tomatoes. 

A  mixture  of  acid  phosphate  and  potassium  sulfate  also  was 
tested  as  a  top-dressing  for  the  tomato  crop.  Other  tests  were  in- 
cluded to  compare  further  nitrate  of  soda  and  dried  blood  as  sources 
of  nitrogen  for  the  crops  in  question. 

The  kinds  of  soil  mixture  used  in  the  various  sections,  or  plots, 
and  the  soil  treatments  applied  are  given  in  Table  18. 


TABLE  18. — SOIL  TREATMENT  OF  THE  DIFFERENT  PLOTS  IN  LETTUCE 
AND  TOMATO  EXPERIMENTS,  1921-1924 


Plot 

Soil 
mix- 
ture 

Treatment 

71 

4-2-1 

Check 

72 

4-2-1 

Nitrate  of  soda 

73 

4-2-1 

Dried  blood 

74 

4-2-1 

Acid  phosphate,  lime 

75 

4-2-1 

Acid  phosphate,  lime,  nitrate 

76 

4-2-1 

Steamed  bone,  nitrate 

77 

4-2-1 

Acid  phosphate,  lime,  potassium  sulfate,  nitrate 

78 

4-2-1 

Nitrate  for  lettuce,  acid  phosphate  for  tomatoes 

79 

4-2-1 

Dried  blood  for  lettuce,  acid  phosphate  for  tomatoes 

80 

4-2-1 

Nitrate  for  lettuce,  acid  phosphate  and  potassium  sulfate  for 

tomatoes 

81 

4-4-1 

Check 

82 

4-4-1 

Sterilized 

83 

4-4-1 

Sterilized;  nitrate  for  fourth  crop  lettuce,  acid  phosphate  for 

tomatoes 

84 

4-4-1 

Nitrate  for  lettuce,  acid  phosphate  and  potassium  sulfate  for 

tomatoes 

The  initial  applications  of  fertilizer  and  the  top-dressings  of  ni- 
trate were  made  in  the  same  manner  as  in  the  preceding  tests.  The 
top-dressings  for  the  tomatoes  (acid  phosphate,  and  acid  phosphate 
and  potassium  sulfate)  were  made  immediately  after  the  fourth  crop 
of  lettuce  was  harvested  from  among  the  tomato  plants.  The  materials 
were  sprinkled  over  the  surface  of  the  soil  and  worked  in  lightly  by 
means  of  a  hand  weeder.  Care  was  taken  to  avoid  letting  any  of  the 
fertilizers  come  in  direct  contact  with  the  stems  or  roots  of  the  plants. 

EFFECT  OF  DIFFERENT  METHODS  OF  APPLYING  PHOSPHORUS 

The  combination  of  steamed  bone  and  nitrate  did  not  result  in  as 
high  yields  of  lettuce  as  an  average  for  the  three  years  as  the  acid 
phosphate  with  nitrate  and  lime  (Table  19).  The  latter  combination 
gave  slightly  better  yields  than  the  average  of  the  three  nitrate  plots, 


330 


BULLETIN  No.  286 


[February, 


TABLE  19. — YIELDS  OF  LETTUCE:     COMPARISON  OF  EFFECT  OF  ACID  PHOSPHATE 
AND  STEAMED  BONE  ADDED  TO  A  4-2-1  SOIL  MIXTURE 


Plot 

Treatment 

1921-22 

1922-23 

1923-24 

3-year 
average 

71 

Check              

Ibs.  —  oz. 
50—12 

Ibs.  —  oz. 
42—  9 

Ibs.  —  02. 

56—  8 

Ibs.  —  oz. 
49—15 

74 

Acid  phosphate,  lime  

52—  6 

47—  2 

60—11 

53—  6 

75 

Acid  phosphate,  lime,  nitrate  

61—11 

53—  8 

69—12 

61—10 

76 

Steamed  bone,  nitrate  

55  —  10 

56  —  12 

59—10 

57—  5 

Average  of  3  nitrate  plots,  without 
phosphorus  (72,  78,  80)  

57—  1 

55—13 

64—14 

59—  4 

while  the  yields  from  steamed  bone  and  nitrate  averaged  slightly  less 
than  the  yields  from  the  plots  treated  with  nitrate  alone. 

The  combined  treatment  of  acid  phosphate,  lime,  and  nitrate  gave 
much  better  average  yields  of  tomatoes  than  the  lime  and  acid  phos- 
phate (Table  20) .  The  top-dressing  of  acid  phosphate  to  the  tomatoes, 
following  nitrate  treatment  for  the  lettuce,  gave  still  better  results. 
Where  dried  blood  had  been  used  as  a  source  of  nitrogen  for  the  let- 
tuce, the  top-dressing  of  acid  phosphate  for  the  tomatoes  did  not  ap- 
pear to  be  effective. 


TABLE  20. — YIELDS  OF  TOMATOES:    EFFECT  OF  DIFFERENT  METHODS  OF 
SUPPLYING  PHOSPHORUS  TO  A  4-2-1  SOIL  MIXTURE 


Plot 

Treatment 

1921-22 

1922-23 

1923-24 

3-year 
average 

71 

Check  

Ibs.  —  oz. 
56—  2 

Ibs.  —  oz. 
71—15 

Ibs.  —  oz. 
70—  0 

Ibs.  —  oz. 
66—  0 

74 

Acid  phosphate,  lime  

45—  0 

73—  3 

58—14 

59—  0 

75 

Acid  phosphate,  lime,  nitrate  

59  —  12 

72—  3 

75—12 

69—  3 

76 

Steamed  bone,  nitrate  

69  —  6 

80  —  5 

73—  2 

74—  4 

77 

Acid    phosphate,    lime,    potassium 
sulf  ate,  nitrate  

62  —  7 

69  —  9 

82—11 

71—  9 

78 

Nitrate  for  lettuce,  acid  phosphate 
for  tomatoes  

71—13 

69—  7 

75—  7 

72—  3 

79 

Blood  for  lettuce,  acid  phosphate 
for  tomatoes  

51—  0 

67—15 

62—  0 

60—  5 

80 

Nitrate  for  lettuce,  acid  phosphate 
and  potassium  sulfate  for  tomatoes 

55—  1 

62—  9 

72—13 

63—  7 

The  highest  yield  of  tomatoes,  as  an  average  for  the  three  years, 
was  secured  from  the  plot  treated  with  steamed  bone  and  nitrate  for 
the  lettuce,  with  no  additional  treatment  for  the  tomatoes.  The  addi- 
tion of  potassium  sulfate  as  a  top-dressing  along  with  the  acid  phos- 
phate seemed  to  reduce  the  yield. 


19271 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


331 


TOP-DRESSINGS  APPLIED  TO  LAST  CROPS  REDUCE  LOSSES 
FROM  STEAM  STERILIZATION 

In  the  previous  tests  steam  sterilization  of  the  soil  before  the 
planting  of  each  lettuce  crop  seemed  to  result  in  such  depletion  of  the 
soil  as  to  reduce  the  fourth  crop  of  lettuce  and  the  crop  of  tomatoes 
following.  A  test  was  therefore  made  to  determine  the  effect  of  the 
addition  of  nitrate  to  the  sterilized  soil  just  before  planting  the  fourth 
crop,  and  of  acid  phosphate  following  the  harvest  of  the  lettuce. 


TABLE  21. — YIELDS  OF  LETTUCE:    EFFECT  OF  STEAM  STERILIZATION 


Plot 

Treatment 

1921-22 

1922-23 

1923-24 

3-year 
average 

81 

Check  

Ibs.  —  oz. 
54—  5 

Ibs.  —  oz. 
54—  9 

Ibs.  —  oz. 
58—13 

Ibs.  —  oz. 
55—14 

82 

Sterilized  .... 

67—  0 

58—11 

68—13 

64—13 

83 

Sterilized;  nitrate  for  4th  crop  .  . 

70—  8 

60—15 

66—  0 

65—13 

84 

Nitrate  

61—  10* 

59—11 

69—  5 

63—  8 

Steam  sterilization  distinctly  increased  the  total  yield  of  lettuce 
each  year,  and  in  two  years  out  of  the  three  the  application  of  nitrate 
of  soda  for  the  fourth  crop  made  a  slight  additional  increase  (Table 
21).  Each  year  the  fourth  crop  was  slightly  larger  from  the  plot  that 
was  treated  with  nitrate  preceding  the  planting  of  that  crop.  However, 
the  fourth  crop  of  lettuce  was  not  reduced  by  the  sterilization  of  the 
soil,  as  it  wras  in  the  preceding  test. 


TABLE  22. — EFFECT  OF  STEAM  STERILIZATION  ON  TOMATO 
CROP  FOLLOWING  LETTUCE 


Plot 

Treatment 

1922 

1923 

1924 

3-year 
average 

81 

Check  

Ibs.  —  oz. 
55—  2 

Ibs.—oz. 
68—10 

Ibs.  —  oz. 
59—12 

Ibs.  —  oz. 
61—  2 

82 

Sterilized  ... 

37  —  15 

38—  3 

54—  9 

43—  9 

83 

Sterilized,   nitrate  for  4th  crop  of 
lettuce,  acid  phosphate  for  toma- 
toes            

47—  9 

50—  7 

61—12 

53—  4 

84 

Nitrate  for  lettuce,  acid  phosphate 
and  potassium  sulfate  for  tomatoes 

71—  3 

71—15 

72—14 

72—  0 

The  depleting  effect  of  steam  sterilization  on  the  soil  during  the 
production  of  the  four  lettuce  crops  was  apparent  in  the  tomato  crop 
following  the  lettuce  (Table  22).  The  sterilized  plot  without  supple- 


332 


BULLETIN  No.  286 


[February, 


mentary  treatment  yielded  a  much  smaller  crop  of  tomatoes,  as  an 
average  for  three  years,  than  the  untreated  plot.  Top-dressings  of 
sodium  nitrate  applied  before  the  last  crop  of  lettuce,  and  of  acid 
phosphate  to  the  tomatoes,  partially  overcame  this  depleted  condition, 
but  still  the  average  yield  of  the  plot  so  treated  was  less  than  the  yield 
of  the  check  plot. 

Top-dressings  of  acid  phosphate  and  potassium  sulfate  applied  to 
the  unsterilized  soil  of  the  same  composition,  following  treatment  with 
nitrate  of  soda  for  the  lettuce,  gave  a  decided  increase  in  yield. 

SODIUM  NITRATE  AND  DRIED  BLOOD  ABOUT  EQUAL  IN  VALUE 
AS  SOURCES  OF  NITROGEN  FOR  LETTUCE 

Each  year  both  sodium  nitrate  used  alone  and  dried  blood  used 
alone  gave  distinct  increases  in  yields  of  lettuce,  as  compared  with  the 
check  plot  (Table  23).  While  the  average  yields  from  the  plots  treated 


TABLE  23. — YIELDS  OF  LETTUCE:   COMPARISON  OF  EFFECT  OF  SODIUM  NITRATE 
AND  DRIED  BLOOD  ADDED  TO  A  4-2-1  SOIL  MIXTURE 


Plot 

Treatment 

1921-22 

1922-23 

1923-24 

3-year 
average 

71 

Check  

Ibs.  —  oz, 
50—12 

Ibs.  —  02. 
42—  9 

Ibs.  —  02. 
56—  8 

Ibs.  —  02. 
49—15 

72  --:• 

Nitrate  

58—  5 

47—15 

64—  5 

56—13 

78 

Nitrate  

57—13 

60—  8 

64—  3 

60—13 

80 

Nitrate  

55—  3 

59—  1 

66  —  2 

60—  2 

Average  of  3  nitrate  plots  

57—  1 

55  —  13 

64—14 

59—  4 

73 

Dried  blood  

62—13 

53—15 

65—  2 

60—10 

79 

Dried  blood  

59—  8 

61—10 

64—  1 

61—11 

Average  of  2  dried  blood  plots  

61—  2 

57—12 

64—  9 

61—  2 

with  blood  were  slightly  higher  for  the  three-year  period  than  those 
from  plots  treated  with  nitrate,  the  data  in  Table  5  indicate  that  for 
the  preceding  three-year  period  the  average  yields  were  slightly  better 
from  the  nitrated  plot.  If  a  six-year  average  is  taken,  the  yields  are 
approximately  the  same  from  the  plots  treated  with  nitrate  and  from 
those  treated  with  dried  blood. 


Two  SOIL  MIXTURES  COMPARED,  WITH  AND  WITHOUT  NITRATE 

The  4-4-1  soil  mixture  (4  parts  each  of  loam  and  manure  and  1 
part  sand)  gave  larger  yields  of  lettuce  every  year  than  the  4-2-1  mix- 
ture, when  neither  soil  was  supplemented  with  additional  nitrogen 


EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES 


333 


TABLE  24. — YIELDS  OF  LETTUCE:   COMPARISON  OF  EFFECT  OF 
Two  DIFFERENT  SOIL  MIXTURES 


Plot 

Soil 
mix- 
ture 

Treatment 

1921-22 

1922-23 

1923-24 

3-year 
average 

71 

4-2-1 

Check  

Ibs.  —  02. 
50  —  12 

Ibs.  —  02. 
42  9 

Ibs.  —  02. 

56       8 

Z6s%.  —  02. 
dO     1  "> 

81 

4-4-1 

Check  

54—  5 

54      9 

58       13 

^     14 

72 

4-2-1 

Nitrate  

58—  5 

47—15 

64--  5 

56     13 

78 

4-2-1 

Nitrate  

57  —  13 

60      8 

64      3 

60     13 

80 

4-2-1 

Nitrate  

55  —  3 

59  —  1 

66      2 

60    •  2 

84 

4-4-1 

Average  of  3  nitrate  plots  .... 
Nitrate  

57—  2 
61—10 

55—13 
59—11 

64—14 
69—  5 

59—  4 
63—  8 

(Table  24) .  The  addition  of  nitrate  to  both  soils  distinctly  increased 
the  yields,  the  4-2-1  mixture  with  the  addition  of  nitrate  giving  larger 
yields  than  the  4-4-1  mixture  without  nitrate.  However,  the  largest 
yields  of  all  were  secured  from  the  4-4-1  mixture  treated  with  nitrate. 
These  results  emphasize  the  importance  of  liberal  supplies  of  nitrogen 
for  the  lettuce  crop. 

COMBINED  YIELDS  OF  LETTUCE  AND  TOMATOES 

In  order  to  determine  the  total  yield  of  lettuce  and  tomatoes  for 
the  greenhouse  cropping  season,  the  yields  have  been  reduced  to  terms 
of  pounds  per  square  foot  of  bench  space  (Table  25). 

The  products  from  the  greenhouse  in  1921  to  1924  were  sold  at 
wholesale  to  merchants  in  Champaign  and  Urbana.  The  price  of  let- 
tuce varied  from  12%  to  23  cents  a  pound,  and  the  tomatoes  were  sold 
at  15  to  20  cents  a  pound.  The  value  of  the  crops  per  square  foot  of 
bench  space  has  been  calculated  on  the  basis  of  18  cents  a  pound 
(Table  25). 

The  value  of  the  combined  crop  averaged  more  than  one  dollar 
per  square  foot  of  bench  space  for  the  highest  yielding  plot,  in  spite  of 
the  lower  price  of  products  in  this  period  as  compared  with  the  pre- 
ceding three-year  period.  Several  other  plots  produced  crops  to  the 
value  of  almost  one  dollar  per  square  foot  of  bench  space. 

On  the  4-2-1  soil  mixture  acid  phosphate  and  lime  used  with  ni- 
trate produced  a  satisfactory  crop  of  lettuce  and  a  good  crop  of  to- 
matoes. Slightly  better  results  in  combined  yields  of  the  two  crops, 
however,  were  secured  when  the  nitrate  was  used  alone  for  the  lettuce 
and  the  acid  phosphate  applied  as  a  top-dressing  for  the  tomatoes  after 
the  last  crop  of  lettuce  was  harvested.  The  use  of  steamed  bone  with 
nitrate  resulted  in  the  largest  crop  of  tomatoes,  but  was  less  favorable 
to  the  production  of  lettuce  than  the  nitrate  and  acid  phosphate. 


334 


BULLETIN  No.  286 


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1927]  EXPERIMENTS  WITH  GREENHOUSE  LETTUCE  AND  TOMATOES  335 

On  the  whole,  it  appears  that  in  growing  lettuce  and  tomatoes  in  a 
4-2-1  soil  mixture,  the  beneficial  effects  of  phosphorus  on  the  tomato 
crop,  without  detriment  to  the  lettuce,  can  be  secured  most  readily 
by  using  nitrate  alone  for  the  lettuce  and  applying  acid  phosphate  as  a 
top-dressing  for  the  tomatoes  after  the  last  crop  of  lettuce  has  been 
harvested. 

Sterilization  of  the  4-4-1  soil  mixture  resulted  in  the  heaviest 
crops  of  lettuce,  but  so  depleted  the  soil  that,  in  spite  of  the  top-dress- 
ings of  sodium  nitrate  and  acid  phosphate,  the  yields  of  tomatoes  were 
much  reduced.  The  unsterilized  4-4-1  mixture  treated  with  nitrate  for 
the  lettuce  and  supplemented  with  a  top-dressing  of  acid  phosphate 
and  potassium  sulfate  for  the  tomatoes,  produced  a  large  crop  of  to- 
matoes and  the  largest  combined  yield  of  tomatoes  and  lettuce. 

COST  OF  FERTILIZER  RELATIVELY  SMALL 

The  question  of  the  relative  costs  of  the  different  fertilizer  treat- 
ments, so  far  as  the  commercial  fertilizers  are  concerned,  is  unim- 
portant, for  at  the  prices  of  fertilizing  materials  in  1924,  the  cost  of 
the  most  expensive  treatment  was  less  than  l/2  cent  a  square  foot.  The 
expense  for  commercial  fertilizer,  therefore,  is  almost  negligible  as  a 
factor  in  the  cost  of  producing  greenhouse  lettuce  and  tomatoes,  when 
the  original  cost  of  the  greenhouse  and  equipment,  the  upkeep  of  the 
plant,  and  the  fuel  and  labor  involved  in  producing  the  crop  are  con- 
sidered. 

Less  than  %  cent  for  supplementary  fertilizer  for  a  crop  that  will 
probably  be  worth  nearly  a  dollar  is  a  very  small  item  in  the  cost  of 
production,  and  the  relative  costs  of  different  commercial  fertilizers 
need  not  be  considered  in  comparing  their  merits. 

CONCLUSIONS 

1.  It  does  not  seem  feasible  to  grow  greenhouse  lettuce  and  toma- 
toes on  raised  benches  of  brown  silt  loam  without  the  use  of  manure. 
Not  only  are  the  yields  light,  but  the  quality  of  lettuce  is  poor  where 
no  manure  is  used. 

2.  Satisfactory  crops  of  greenhouse  lettuce  and  tomatoes  may  be 
grown  in  a  soil  mixture  of  4  parts  brown  silt  loam,  2  parts  rotted 
manure,  and  1  part  sand  by  properly  supplementing  this  mixture  with 
commercial  fertilizers. 

3.  Greenhouse  lettuce  responds  readily  to  nitrogen  treatment.  Ni- 
trate of  soda  or  dried  blood  will  give  excellent  results  in  supplementing 
the  plant-food  materials  in  a  4-2-1  soil  mixture.    Nitrate  will  even 
increase  the  yield  of  lettuce  on  a  rich  soil  mixture  composed  of  4  parts 
loam,  4  parts  rotted  manure,  and  1  part  sand. 


336  BULLETIN  No.  286 

4.  When  used  on  a  4-2-1  soil  mixture,  acid  phosphate  is  detri- 
mental to  the  lettuce  crop  unless  it  is  used  in  combination  with  lime, 
but  is  beneficial  to  the  tomato  crop,  especially  when  used  in  combina- 
tion with  nitrate.  The  beneficial  effect  on  the  tomatoes  may  be  secured 
without  danger  of  detriment  to  the  lettuce  by  applying  the  acid  phos- 
phate as  a  top-dressing  for  the  tomatoes  after  the  last  crop  of  lettuce 
has  been  harvested.    Such   fertilization,   combined  with  the  use  of 
sodium  nitrate  in  the  production  of  the  lettuce,  results  in  conditions 
favorable  for  the  production  of  both  crops. 

5.  Potassium  sulfate  appears  to  be  of  no  particular  importance  in 
the  fertilizing  of  greenhouse  lettuce,  but  may  be  of  some  benefit  to 
greenhouse  tomatoes,  when  used  in  combination  with  sodium  nitrate 
or  nitrate  and  acid  phosphate. 

6.  If  excessive  quantities  of  commercial  fertilizers  are  used,  the 
yields  of  both  lettuce  and  tomatoes  are  likely  to  be  reduced. 

7.  Since  the  cost  of  commercial  fertilizer  is  an  insignificant  item 
in  the  cost  of  production  of  greenhouse  lettuce  and  tomatoes,  the  use 
of  such  materials  as  will  increase  the  yields  is  fully  warranted. 

8.  Sterilizing  a  heavily  manured  soil  by  the  use  of  steam  before 
each  crop  of  lettuce  is  planted  stimulates  an  enormous  growth  of  let- 
tuce, especially  in  the  second  and  third  crops,  but  results  in  such  ex- 
haustion of  the  soil  that  the  succeeding  crop  of  tomatoes  is  likely  to 
be  small. 


UNIVERSITY  OF  ILLINOIS-URBANA 


